Generally, for writing instruments such as oil-based ball-point pens, water-based ball-point pens, a removable cap for protecting the front end of the writing part by enclosing it when unused is provided.
Particularly, in some kinds of writing instruments, in order to prevent ink at the writing part from drying, the tip part is hermetically enclosed by the cap so that the part can be isolated from the outside air.
(Background Art 1)
As one of the conventionally known writing instrument configurations, a refill (replacement pen element) which is formed of a point assembly and an ink tank by engaging one with the other, is accommodated, on its tip side, into a front barrel, and on its ink tank side, into a rear barrel, forming an joined writing instrument structure of the front and rear barrels with the writing tip projected from the front barrel.
There is also another known configuration in which a front barrel is joined with a point assembly to bean integrated structure while a cartridge type ink tank (refill) is provided in the rear side of the front barrel, thereby forming a writing instrument body by screw engagement of the rear barrel with the front barrel.
However, with the former writing instrument body configuration, looseness at the connection between the front and rear barrels causes unstable retention of the refill, giving rise to a problem of the writing tip rattling.
On the other hand, the latter writing instrument body configuration has no rattling problem at the writing tip because the front barrel and the point assembly are integrally formed, but has a problem of lower ink capacity. More explicitly, since the ink cartridge is fitted to the attachment of the front barrel, the inside diameter of the ink cartridge should be smaller by the thickness of the attachment than the outside diameter of the front barrel, hence the volume of ink to be filled into the cartridge becomes lower. In order to increase the ink capacity of the ink cartridge, it is necessary to make the outside diameter of the attachment greater and so the rear barrel thicker. However, this means increase in differential outside diameter between the front barrel and the attachment, causing the problem of the external appearance of the writing instrument body being spoiled. Further, enlargement of the attachment results in exposure of the attachment beside the cap and the rear barrel, further degrading the external appearance of the writing instrument body.
(Background Art 2)
In some known writing instruments, the outer periphery of the writing instrument body is often printed with the maker name, trade name, model name and the like or covered with a thin film with these printed thereto.
In a case of a writing instrument having a cap as a separate part, the cap is fitted to the rear end of the writing instrument body when it is used.
However, in a case where a writing instrument body having the outer periphery printed with the maker name, trade name, model name and the like or covered with a thin film with these printed thereto is used for writing, the fitting portion of the cap rubs the outer periphery of the writing instrument body every time the cap is fitted to the rear end of the writing instrument body, so that there occurs the problem that the thin film may peel off from its rear end or the print may become faint and patchy.
To deal with this, there are some known conventional configurations in which a stepped portion is formed in the rear part of the writing instrument body so that the cap can be easily fitted while no print is located at that area.
However, these conventional configurations suffer from the problem of complexity in the shape of the writing instrument body and degradation of the external appearance.
(Background Art 3)
As an example of a writing instrument cap, a configuration disclosed in Japanese Utility Model Application Laid-open Sho 57 No. 193587 can be mentioned.
This writing instrument cap has a configuration in which an engaging piece formed with a clip of the cap is press fitted into a vertical hole formed in an projection from the peripheral side of a writing instrument or the like, and the vertical hole is formed so as to have an approximate arc shaped cross-section while the engaging piece of the clip is formed so as to have an approximate rectangular cross-section.
In the assembly work of the writing instrument cap into the writing instrument, it is necessary to make two actions in parallel, i.e., adding a stress on the clip so that it elastically deforms and squeezing the clip into the vertical hole, in order to enable the clip to be held in the vertical hole with the necessary gripping force. Therefore, the fitter needs skill for the assembly work and also suffers from a hard burden on their fingers because a strong force should be applied to a small portion.
Further, in the case where the cross-section of the clip is arc shaped, the clip should be elastically deformed opposing its strong elasticity. In anyway, it is difficult to automate these assembly steps.
Under the consideration of the above conventional problems, it is an object of the present invention to provide a writing instrument which is free from rattling of the point assembly and still can secure a large ink capacity without spoiling the external appearance.
It is another object of the present invention to provide a writing instrument cap which can be fitted without degrading the print on the writing instrument body and yet can be fitted easily without spoiling the external appearance.
It is still another object of the present invention to provide a writing instrument cap which facilitates assembly of a cap body and a clip, no matter what the cross-section of the clip is, can be suitable for automation and yet stylish, as well as providing an assembly method thereof.